The goal of this project is to study the distribution of the calcitonin gene-related peptide-immunoreactive (CGRP-IR) primary afferent fibers in the intact rat gastric mucosa and around experimental stress ulcers. The varicose CGRP-IR fibers run toward the luminal epithelium in the lamina propria in close connection with blood vessels and smooth muscle cells suggesting a functional, neurochemical relationship between them. The nerve fibers' branching pattern suggests the presence of columnar neurovascular regulatory units in the mucosa that are oriented perpendicular to the lumen. We found a number of CGRP-producing (probably non-neuronal) cells of at least two types located mainly near the border between the mucosa and submucosa. Since these cells are also present in variable positions following stress ulcer induction, it seems that at least two different systems, a neural and a non-neural, are responsible for the CGRP trophic support of the gastric wall. Our observations also help confirm the theory that CGRP may play a role in the development of local vasodilation, congestion and therefore in mucosal damage associated with the stress ulcers.